[1] Karlsruhe Inst Technol, Inst Nanotechnol INT, D-76128 Karlsruhe, Germany
[2] Karlsruhe Inst Technol, Karlsruhe Nano Micro Facil, D-76128 Karlsruhe, Germany
[3] Karlsruhe Inst Technol, Inst Biol Interfaces IBG 1, D-76128 Karlsruhe, Germany
[4] Univ Munster, Inst Phys, D-48149 Munster, Germany
[5] Univ Munster, Ctr Nanotechnol CeNTech, D-48149 Munster, Germany